[this has been updated here)
Some people sadly, do not vote (which is a great pity and not very effective, as you will see) and some do vote. Of those that do, some vote for the same party each and every time, and some do not. This latter group are called swing voters. If you are a swing voter, read on.
The sapient swing voter needs first of all to find out if the seat is "safe". If it is, all votes apart from those for the incumbent are "wasted" in the sense that they do not get any representation in Parliament. There's FPTP for you. It is a crap system, and it has to go.
In a safe seat, then you might as well vote for your principles.The best signal to send is with a Green Party vote, because it signals your wish for radical reform of our political and economic system, along rational lines. In other words, you get more bangs for your ballot than voting something like UPIK (who are the new MRLP) or Pirate, despite their romantic and Depp-like attractions.
If on the other hand you are in a marginal constituency, then I as a Green would strongly urge you to vote Green, if that option is open, since your vote will lever the winner to be more green in Parliament so as to win your vote back.
But I recognise that tactical voting is very appealing in a marginal seat, and here surely any thinking voter will wish to vote ABT (Anything But Tory). If you are presented with a choice between Labour and LibDem, then back the LibDem in the hope of getting a well-hung Parliament, with Vince Cable in the Treasury, and Proportional Representation well and truly on the menu.
All voters who care about democracy and political reform are recommended to murmur the words "First Past the Post Has Got To Go" to the clerks as they hand you your precious polling form.
I hope this is helpful.